Named capture groups may be specified using the /(?<name>pattern)/u
syntax, with named backreferences specified as /\k<name>/u. They're
hidden behind the --harmony-regexp-named-captures flag, and are only
enabled for unicode regexps.
R=yangguo@chromium.org
BUG=
Review-Url: https://codereview.chromium.org/2050343002
Cr-Commit-Position: refs/heads/master@{#36986}
